PERINATAL THYROID FUNCTION IN THE RAT

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Abstract
Thyroid function in the developing rat was measured during late gestation and the first 3 weeks of life. Radioiodine uptake showed a marked peak immediately after birth. Thyroidal hormone stores dropped to stable levels by the 4th day of life and an increase in hepatic [alpha]-glycerophosphate dehydro-genase activity suggested increased hormone secretion about the time of birth. Monoiodotyrosine in the thyroid glands declined sharply just before birth but recovered its prenatal level by the 3rd day of life. The data may indicate a discharge of pituitary TSH [thyroid stimulating hormone] at birth followed by a period of pituitary hormone repletion. Hypothalamic influences upon the thyroid-pituitary axis appear to be of little importance in perinatal life.